Watching the Skies » Derecho

More info on today’s incredible mid-west derecho

Sean Toner — Fri, 08 May 2009 23:10:23 +0000

Here is a blog entry made by the CIMSS Satellite Blog folks on today’s extremely powerful derecho event in the mid-west. At one point, the storm looked like a hurricane from both the radar and satellite views with an incredible comma shape precip echo on radar that nearly wrapped around the entire storm and traverse banding spreading out from the upper layers of the storm. See one of my previous posts for a screenshot of radar reflectivity earlier.

http://cimss.ssec.wisc.edu/goes/blog/archives/2534

At 18:25 GMT a wind speed of 106mph was measured in Illinois and hail up to 2.75 inches measured in Missouri at 14:34 GMT. Now THAT is an incredible derecho!

Bow echo transformation into something strange!

Sean Toner — Fri, 08 May 2009 17:14:39 +0000

Today I captured this absolutely amazing looking bow echo storm that transformed into a, well quite frankly I have no idea what you would consider this. This looks more like a major rain wrap around a low pressure system, or even to a degree like a hurricane. Take a look at this crazy storm. This thing could still be considered a derecho event too as it was putting out very impressive winds, several tornado reports and hail.

UPDATE: So apparently this is could be called a comma shaped bow echo, generally considered to be the last stage in evolution of a bow echo storm. I haven’t seen anything like it before, looks incredible to me.

Storm threat just barely missed Frisco, has passed.

Sean Toner — Wed, 06 May 2009 11:26:03 +0000

The worst of this storm just clipped us and went into McKinney, which is good because this storm was a pretty potent storm. This storm complex is at least three separate bow echo storms joined together to form a line. The one that just passed over McKinney was showing signs of strong rotation and had a nice hook echo on the front of the storm, so it’s probably a good thing this one missed Frisco.

Anyways, the severe threat has appeared to of passed Frisco. We still may get occasional lightning strikes and strong wind gusts but the bulk of the activity stayed just a few miles east. This storm complex will be traveling to the SE and continue to affect eastern portions of the metroplex.

Now maybe i can go back to sleep.

Severe Thunderstorm Warning and Watch for Frisco TX

Sean Toner — Wed, 06 May 2009 10:45:42 +0000

OK so the weather radio just put a stop to my sleep tonight. Glad I woke up though, this one is a big one. Line of severe storms is producing very strong to severe winds, moving SSE at 35 knots. The storms are 15 miles north so this puts an ETA of around 25 minutes, or 6:05am. Again, these storms are putting out winds of up to 65 knots, I can definitely verify this on radar. There is also rotation in one of the storms approaching our area so be advised this storm is extremely strong. The SPC also notes this bow echo storm is a possible derecho. Warning and watch details below:

BULLETIN – EAS ACTIVATION REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE FORT WORTH TX
533 AM CDT WED MAY 6 2009

THE NATIONAL WEATHER SERVICE IN FORT WORTH HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR…
COLLIN COUNTY IN NORTH CENTRAL TEXAS…
GRAYSON COUNTY IN NORTH CENTRAL TEXAS…

* UNTIL 630 AM CDT

* AT 533 AM CDT…NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
LINE OF SEVERE THUNDERSTORMS CAPABLE OF PRODUCING NICKEL SIZE
HAIL…AND DAMAGING WINDS IN EXCESS OF 60 MPH. THESE STORMS WERE
LOCATED ALONG A LINE EXTENDING FROM BELLS TO 5 MILES SOUTH OF
COLLINSVILLE…AND MOVING SOUTH AT 30 MPH.

* SEVERE THUNDERSTORMS WILL BE NEAR…
TOM BEAN…HOWE AND GUNTER BY 540 AM
WHITEWRIGHT BY 545 AM
VAN ALSTYNE BY 550 AM
CELINA AND ANNA BY 600 AM
PROSPER BY 610 AM
MCKINNEY AND FRISCO BY 620 AM

PRECAUTIONARY/PREPAREDNESS ACTIONS…

FOR YOUR PROTECTION MOVE TO A STURDY SHELTER UNTIL THE STORM HAS
PASSED.

URGENT – IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 252
NWS STORM PREDICTION CENTER NORMAN OK
530 AM CDT WED MAY 6 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHWESTERN ARKANSAS
NORTHWESTERN LOUISIANA
SOUTHERN OKLAHOMA
NORTH-CENTRAL…NORTHEASTERN AND EASTERN TEXAS

EFFECTIVE THIS WEDNESDAY MORNING AND AFTERNOON FROM 530 AM UNTIL
100 PM CDT.

HAIL TO 1 INCH IN DIAMETER…THUNDERSTORM WIND GUSTS TO 80
MPH…AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 55 MILES WEST
SOUTHWEST OF ARDMORE OKLAHOMA TO 60 MILES NORTHEAST OF
NATCHITOCHES LOUISIANA. FOR A COMPLETE DEPICTION OF THE WATCH
SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).

REMEMBER…A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION…THIS SEVERE THUNDERSTORM WATCH REPLACES
SEVERE THUNDERSTORM WATCH NUMBER 249. WATCH NUMBER 249 WILL NOT
BE IN EFFECT AFTER 530 AM CDT. CONTINUE…WW 248…WW 251…

DISCUSSION…INCREASINGLY WELL-ORGANIZED BOW ECHO IN FORMER WW 249
IS BEGINNING TO PRODUCE SVR GUSTS ABOVE 50 KT AS IT MOVES OVER AND S
OF SFC WARM FRONT OUTLINED IN MESOSCALE DISCUSSION 727. THIS MCS
SHOULD CONTINUE TO SURGE SEWD WITH POTENTIAL FOR SWATH OF DAMAGING
WIND…POSSIBLE DERECHO…OVER PORTIONS WW AREA. COUNTY WW AREA
FANS OUTWARD WITH SEWD EXTENT TO ACCOUNT FOR POTENTIAL
SPREAD/EXPANSION OF DRIVING COLD POOL.

AVIATION…A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70 KNOTS.
A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 600. MEAN STORM MOTION
VECTOR 30040.

Severe weather likely Friday – possibly a derecho event?

Sean Toner — Fri, 01 May 2009 07:13:04 +0000

Friday's severe weather outlook looks to place the bulk of the severe action right in our neighborhood with the best risk of severe weather anywhere from the DFW Metroplex through to the western North Texas region. Currently the SPC has us under a 'Slight' risk, but they have noted in their forecast discussion this may very well be increased to a 'Moderate' risk once these thunderstorm complexes begin to initiate.

At this time, we are looking at our primary risk time being in the afternoon to evening hours with storms similar in nature to what we experienced last night. These storms will likely form to our west and become a large MCS again, develop a large cold air pool which creates a mini cold front that will push our way, and create a line of severe thunderstorms. Forecast MLCAPE values of 3000 – 4000 J/KG makes for an incredibly unstable atmosphere, so when storms develop, they will become severe very quickly.

The NWS office in Fort Worth notes that the scenereo that is likely to play out for Friday has similarities to the June 1 2004 derecho event that occured in the metroplex. A derecho simply put, is a large line of severe thunderstorms over 100 kilometers wide that produce extremely strong winds generally exceeding 64 knots, last for numerous hours and generally travel well over 400 kilometers. Derechos can produce similar types of wide spread wind damage that you might find from a category 2 hurricane. The event that occured here on June 1 2004 caused large ammounts of building, tree, power line damage, and left over 500,000 residents of the metroplex without power. At least 79 severe weather reports were received by the NWS office in Fort Worth from this one event! Again, if a derecho event were to occur, the main risk is extremely strong straight line winds with a good possibility of very large hail as well.

Currently the SPC has us under a 30% hail risk with a 10% risk of 2 inch hail or larger, 30% wind risk and 5% tornado risk. Again, as we progress later in the day Friday, these values are likely to be adjusted. Tomorow will very likely be a severe weather day for the metroplex, so I will send out updates as the scenereo unfolds.

The severe weather threat will continue through Saturday and Sunday when this weather pattern finally sweeps out of the area. Saturday brings a 30% chance of thunderstorms, Sunday has a 60% chance of storms. The storms this weekend will most likely bring very heavy rain, and the NWS in Fort Worth mentioned that a Flood Watch may be needed for our area on Saturday and Sunday. Areas currently swamped from the ~15 inches of rain dumped on Thursday are likely going to receive the heaviest rain this weekend so any flooding conditions now are likely to get worse.

Is everyone liking spring time in Texas yet?! Nothing like this ever occurs in Florida this regularly!